Diffused junction solar cells have been developed having homogeneous as well as double-diffused (selective) emitter structures. Homogeneous emitter structures have the same doping level under passivated and metal (e.g. finger contact) regions. In contrast, double-diffused emitter structures have relatively high doping levels under and aligned with the metal regions (also known as the metal grid) and lower doping levels between these regions. The highly doped regions repel minority carriers (holes) from the metal contacts. This arrangement provides good contact performance and low recombination losses. High efficiency solar cells have been achieved using double-diffused emitter structures.
FIG. 1 is a schematic illustration of a photovoltaic structure 20 including a double-diffused emitter structure. The emitter layer includes n+ regions 22 between n++ regions 24. The highly doped n++ regions are directly below metal fingers 26. The structure 20 further includes a dielectric anti-reflective coating (ARC) layer 28 adjoining one side of the emitter layer and a p-type silicon substrate 30 adjoining the opposite side thereof. The silicon substrate functions as an absorber layer. The fabrication process for forming photovoltaic structures including double-diffused emitters is relatively expensive because of the process complexity and high temperatures required for the process.